The present invention is directed to a device for delivery of medicament, and in particular to a jet injector with a short needle to reduce the pressure at which the jet injector must eject the medicament for proper delivery.
A wide variety of needleless injectors are known in the art. Examples of such injectors include those described in U.S. Pat. No. 5,599,302 issued to Lilley et al., U.S. Pat. No. 5,062,830 to Dunlap, and U.S. Pat. No. 4,790,824 to Morrow et al. In general, these and similar injectors administer medication as a fine, high velocity jet delivered under sufficient pressure to enable the jet to pass through the skin.
As the skin is a tissue composed of several layers and the injector is applied to the external surface of the outermost layer, the delivery pressure must be high enough to penetrate all layers of the skin. The layers of skin include the epidermis, the outermost layer of skin, the dermis, and the subcutaneous region. The required delivery pressure is typically greater than approximately 4000 p.s.i. (27,579 kPa) (measured as the force of the fluid stream divided by the cross-sectional area of the fluid stream).
Although this pressure is readily achievable with most injectors, there are some circumstances in which delivery of medicament to the subcutaneous region under a reduced pressure is desirable. For example, drugs that require a specific molecular structural arrangement, such as a linear protein configuration, may be rendered ineffective due to shear forces caused by the delivery of the drug at high pressures that alter the structural arrangement of the drug. As it is more difficult to deliver a large volume of fluid at a high pressure compared to a small volume, using a lower pressure facilitates delivery of a larger volume of fluid. Furthermore, the lower pressure could make manufacturing an injector device less expensive. The lower pressure would also reduce adverse stresses on the device and result in a corresponding increased useable device lifetime. Moreover, the lower pressure would make jet injection compatible with medicament stored and delivered in glass ampules, which typically cannot withstand the pressure typically reached by jet injectors.
One of the advantages associated with jet injectors is the absence of a hypodermic needle. Given the aversion to needles possessed by some, the absence of a needle provides a psychological benefit. Even devices that utilize conventional hypodermic needles have attempted to capitalize on this psychological benefit. For example, self-injectors or auto-injectors like the ones disclosed in U.S. Pat. Nos. 4,553,962, 4,378,015 and PCT International Publication No. WO 95/29720, WO 97/14455 have retractable needles which are hidden until activation. Upon activation, the needle extends from the bottom of the device and penetrates the user""s skin to deliver medicament. As none of these devices involves delivery of the medicament using jet injection, the medicament delivery location is limited by the length of the needle. For example, if delivery in the subcutaneous region is desired, the needle must be long enough to reach the subcutaneous region. Furthermore, as auto-injectors operate like syringes, the injection time is several seconds or longer. In contrast, jet injectors typically inject in fractions of a second.
U.S. Pat. No. 5,304,128 to Haber et al. describes a jet injecting syringe that uses a short needle to assist injection. The syringe uses a gas powered driven plunger to force medication through the syringe and out of the needle. The needle is retracted until the syringe is activated and then is extended to puncture the skin of the person injected. However, the needle remains extended after the syringe is used. The extended needle could lead to potential biohazards and safety concerns, such as accidental injections and spreading of diseases. Also, the gas powered plunger is both complicated and expensive to manufacture.
PCT Publication No. WO 99/03521 of Novo Nordisk discloses an undefined concept of xe2x80x9cjetxe2x80x9d injection. However, this publication does not teach one the details of the driving mechanism necessary to practice the concept.
PCT Publication No. WO 99/22790 of Elan Corporation teaches a needle assisted injector having a retractable shield that conceals the needle both before and after use of the injector. The disclosed injector has a driving mechanism that operates on pressure created by a chemical reaction. Because of this chemically operated driving mechanism, the injecting time for the injector is at least three seconds and more likely greater than five seconds. This relatively long injection time may create discomfort in the patient receiving the injection. Also, the needle may move during the lengthy injection and add to the patients discomfort.
Even with minimally invasive medical procedures, it is advantageous to maintain the time for the procedures at a minimum. Thus, there exists a need for a needle assisted jet injector that operates at relatively low pressure and that is capable of quickly delivering medicament. There also exists a need for such an injector having a retractable or concealed needle to prevent the medical hazards associated with exposed needles.
The present invention relates to a needle assisted jet injector. In one embodiment, the injection device includes a housing; a retractable injection-assisting needle at a distal end of the injector; a nozzle assembly defining a fluid chamber having an opening for slidingly receiving at least a portion of the needle and being removably associated with the housing; a plunger movable in the fluid chamber; a trigger assembly; and a force generating source operatively associated with the trigger assembly so that movement of the trigger assembly activates the energy source to move the plunger in a first direction to expel a fluid from the fluid chamber. The retractable injection-assisting needle has a needle tip located at a distal end of the needle with at least a portion configured and dimensioned to slide through the nozzle assembly opening; a discharge channel within the needle tip and terminating in an orifice through which the fluid is expelled; a body portion to direct fluid towards the discharge channel; a plunger receptor configured and dimensioned to receive at least a portion of the plunger; and a retraction element operatively associated with the needle and disposed substantially within the nozzle assembly. The needle is located within the nozzle assembly in a retracted position prior to activation of the force generating source. Movement of the plunger in the first direction upon activation of the energy source results in at least a portion of the needle tip extending beyond the nozzle assembly opening to a needle insertion point and expelling the fluid through the needle tip and past the needle insertion point to a needle injection site. The needle insertion point is located at the needle tip, and the needle injection site is distal to the needle tip. The retraction element returns the needle tip to the retracted position after activation of the energy source.
The retraction element may be a resilient O-ring, a spring, or a flexible membrane which moves to allow extension of the needle tip beyond the nozzle assembly opening and then returns to its original position to return the needle tip to its retracted position. The needle body can have an exterior surface which includes a ridge or recess for accommodating the retraction element. A shoulder can be disposed between the needle tip and the needle body for accommodating the retraction element. Preferably, the needle tip, when extended, has a length of approximately 1-5 mm.
In a preferred embodiment, the jet injector includes a housing having distal and proximal ends; a fluid chamber having a seal at one end and located within the housing for holding at least about 0.02 ml to 3 ml of a medicament; an injection-assisting needle having an injecting end and a piercing end and coupled to the distal end of the housing; a plunger movable within the fluid chamber; a force generating source capable of providing sufficient force on the plunger to eject an amount up to about 3 ml of the medicament from the fluid chamber in less than 2.75 seconds; a needle guard located at the distal end of the housing for concealing the needle, the needle guard being moveable between a protecting position and an injecting position; and an activation element operatively associated with the needle guard. The needle is moveable between a medicament storing position and a medicament delivering position. When the needle is in the medicament storing position, it is isolated from the fluid chamber. When the needle is in the medicament delivering position, the piercing end punctures the seal to provide a fluid pathway from the fluid chamber through the needle. Retraction of the needle guard exposes the injecting end of the needle to an insertion point and activation of the force generating source moves the plunger to expel medicament from the fluid chamber and thereby eject the amount of the medicament through the injecting end of the needle and past the needle insertion point to an injection site in less than 2.75 seconds. The needle insertion point is located at the injecting end of the needle, and the injection site is distal to the injecting end of the needle.
Retraction of the needle guard from the protecting position to the injecting position may activate the force generating source, which provides sufficient force to eject an amount of about 1 to 2 ml of the medicament in less than about 2.5 seconds. The jet injector can also include a locking element associated with the needle guard for locking the needle guard in the protecting position after activation of the injection device and after return of the needle guard to the protecting position, to prevent re-exposure of the needle.
The activation element can include an inner housing located inside the housing and having trigger projections for maintaining the plunger in an idle position; and a latch located inside the housing and circumferentially surrounding the inner housing, the latch being moveable between a firing position and an armed position. Retraction of the needle guard to the injecting position urges the latch toward the firing position, thereby releasing the trigger projections from the plunger and activating the injection device.
The jet injector can further include an elastomeric element, such as a spring element, that acts upon the needle guard and urges the needle guard toward the protecting position; wherein the elastomeric element returns the needle guard to the protecting position after the medicament has been ejected from the needle, thereby substantially re-enclosing the needle.
The needle is mounted on a needle holder operatively associated with the needle and the distal end of the housing, such that rotation of the needle holder places the needle in fluid communication with the fluid chamber. Preferably, the needle has a tip with a length of approximately 1-5 mm and the medicament is ejected at a pressure between around 100 to 1000 p.s.i. (689 to 6895 kPa) and at a rate of at least 0.40 ml/sec.
The jet injector may also include a removable safety cap operatively associated with the distal end of the injection device such that rotation of the safety cap imparts rotation on the needle. At least a portion of the housing is made of a transparent or translucent material for allowing viewing of the fluid chamber. The medicament is preferably ejected at a pressure between around 100 to 500 p.s.i. (689 to 3448 kPa) and at a rate of about 0.50 ml/sec so that about 1 ml of the medicament is ejected in about 2 seconds.
The fluid chamber may comprise an ampule having a distal end, a proximal end and an opening in each of the distal and proximal ends; a pierceable seal associated with the opening in the distal end; and a stopper located in the proximal end of the ampule for maintaining the medicament inside the ampule. An alternative fluid chamber may be used such that activation of the force generating source moves the pierceable seal towards the injection assisting needle to pierce the seal and moves the stopper to eject medicament from the injection assisting needle.
The present invention also relates to a method of delivering medicament to an injection site of a patient. The method includes the steps of extending a needle from a shield prior to inserting the needle into the needle insertion point, the shield initially concealing the needle; inserting the needle into the needle insertion point to a depth of less than 5 mm, with the needle being in fluid communication with a fluid chamber that contains at least about 0.02 to 2 ml of the medicament; and applying a force sufficient to eject the medicament from the fluid chamber and through the needle to deliver the medicament to the injection site in less than about 2.75 seconds. The needle insertion point is located more superficial than the injection site.
Preferably, the initial pressing of the shield against the injection site causes activation of the energy mechanism and may establish fluid communication between the needle and the fluid chamber. An additional step includes retracting the needle into the shield after the desired amount of medicament has been delivered to the injection site and wherein the applied force for injecting the medicament is sufficient to eject an amount of about 1 to 2 ml of the medicament in less than about 2.5 seconds. The needle has a length of approximately 1-5 mm and the medicament is ejected at a at a pressure between around 100 to 1000 p.s.i. (689 to 6895 kPa) and at a rate of at least 0.40 ml/sec. Preferably, the medicament is ejected at a pressure between around 100 to 500 p.s.i. (689 to 3448 kPa) and at a rate of about 0.50 ml/sec so that about 1 ml of the medicament is ejected in about 2 seconds.